Catalysed gas-liquid chemical processes



United States Patent Utilice 3,052,713 Patented Sept. 4, 1962 3 052,713 CATALYSED GAS-LHQHD Cmd/MCA@ PROCESSES Hubert .lowitn Hull, England, assigner to The Distillers Company Limited, Edinburgh, Scotland, a British com- Damy Filed Feb. 24, 1959, Ser. No. 795,262 Claims priority, application Great Britain Mar. 5, 1958 Claims. (Cl. 26d- 484) The present invention relates to catalysed chemical processes in which a liquid is reacted with a gas or vapour and in which the rate of reaction is dependent on the concentration of catalyst used.

Many catalysed reactions of this type are known. It is frequently found that while a good yield of the desired product can be obtained, the optimal catalyst concentration required is so great as to make commercial Working of the reaction impracticable; if, however, a sub-optimal concentration of catalyst is used, commercial working of the reaction is again impracticable, because poor yields of the desired product are obtained. Furthermore, in some catalysed reactions of this type, it is desirable to ensure that substantially complete conversion of the gaseous or vapour-phase reactant takes place, without having to use an excessively large contact area between the reactants.

The reaction between ketene and a dialkoxymethane to produce an alkyl 3-alkoxypropionate, for instance, can be catalysed by boron trifluoride, which may conveniently be used in the form of its diethyl ether complex, BF3.C2H5OC2H5. The rate of reaction is dependent on the catalyst concentration. When, for example, ketene is passed up a vertical, jacketed, packed column into the top of which a stream of diethoxymethane containing the catalyst is fed, it is economically undesirable to use more than about 2% by weight of the catalyst in the column; a high yield of the desired product, ethyl 3-ethoxypropionate, may be obtained based on the ketene absorbed, but, using a column of convenient size, only a minor proportion of the ketene fed to the column is absorbed, the remainder passing out of the column in the effluent gas stream, from which it can be recovered and recycled to the column onlyr with great diliiculty. The ketene absorption could, in theory, be increased by using a greater catalyst concentration but this would make commercial working of the process uneconornic.

It is an object of the invention to provide a commercially practicable process of calrying out a reaction of this type whereby a high conversion of the gaseous reactant is achieved.

Accordingly, the present invention is a process of reacting a liquid reactant with a gaseous reactant in the presence of a catalyst to produce a desired product, the rate of reaction being dependent on the concentration of catalyst present, which comprises passing the gaseous reactant through a series of two zones, mixing a portion of the liquid reactant with gaseous reactant in a first Zone containing insuiiicient catalyst to convert substantially all the gaseous reactant present in the iirst zone to the desired product, passing the resulting gaseous material from the lirst zone and mixing it with another portion of the liquid reactant in a second zone containing Sunicient catalyst to convert substantially all the gaseous reactant present in the second zone to the desired product, and recovering the desired product. By the words gaseous reactant in this specification is meant a gas or a vapour; similarly the gaseous material passed from the first zone, as described in the previous paragraph, may be a gas, a vapour or a gas-vapour mixture.

' The series of two Zones through which the gaseous reactant passes may take any suitable form; it may, for example, be two zones of a packed column or a series of separate pot reactors, or separate groups of pot reactors, arranged in cascade form. The two zones may be adjacent or separate. The two zones may be maintained at the same temperature or at different temperatures; in one embodiment ofthe invention, the second zone is maintained at a lower temperature than is the first zone.

The catalyst may be placed in the zones before the gaseous reactant or the liquid reactant is passed through. The catalyst may also be introduced into the zones in adrnixture with the liquid reactant, so that portions of the liquid reactant containing a Vdierent concentration of catalyst are introduced into either of the zones. The concentration of catalyst in the first Zone is such that it iS insuliicient to convert substantially all thek gaseous reactant present in the lirst zone to the desired product, The concentration of catalyst in the portion of the liquid reactant fed to the second zone is such that the catalyst present in that zone is in at least a concentration suidcient to convert substantially all the gaseous reactant present in the second Zone to the desired product. The catalyst may also be introduced into the zones, for example, when the second zone is situated above the rst zone, by feeding into the second zone a mixture of the liquid reactant and catalyst and by feeding into the rst Zone liquid reactant without catalyst, the concentration of catalyst in the feed to the second zone being such that, when the catalyst has become distributed between the two Zones and diluted in the first zone, the iirst zone contains insuiiicient catalyst to convert substantially all the gaseous reactant present to the desired product while the second zone contains suliicient catalyst to convert substantially all the gaseous reactant present to the desired product.

The desired product may be recovered in any suitable way. The eflluent from the rst zone may, for instance, be collected and unwanted by-products removed from it. The product may then be further purilied if necessary.

Presently preferred illustrative embodiments of the invention are shown diagrammatically in the acccompanying drawing, wherein:

FIGURE l represents one such embodiment of the invention, Y

FlGURE 2 represents an alternative embodiment.

ln the embodiment of the invention shown in FIGURE l, ketene vapour is reacted in countercurrent with dif ethoxymethane, introduced as liquid reactant, to yield ethyl 3ethoxypropionate as the desired product, a high conversion of the ketene to ethyl 3-ethoxypropionate being achieved. r[he catalyst is preferably boron triliuoride; the boron trilluoride may be in the form of the diethyl ether complex BFBCZH5OC2H5, 4but other boron trifluoride complexes or gaseous boron triliuoride may be used.

Ketene vapour is fed by the line 1 into the base of the vertical packed column 2 surrounded by the jacket 3 through which a fluid such as water can be circulated to maintain the temperature of the column 2 at a desired level. The column 2 is provided with inlet lines 4 and 5 and outlet lines 6 and 9. A mixture of diethoxymethane with the catalyst is fed as liquid into the colum-n by the lines 4 and 5, and this mixture ows down the packed column, meeting and mixing with the rising ketene vapour.

In operation, water is circulated through the jacket 3 to maintain the column 2 at a temperature of about 50 C. Ketene is introduced into the base of the column by line 1.

Diethoxymethane containing in solution 5% by weight of the catalyst is fed in at the top of the column 2 by line 4 and diethoxymethane containing no catalyst is fed into the lower part of the column 2 by line 5. The portion of the diethoxymethane fed into the column 2 by the line 4 is about 40% of the total diethoxymethane fed in by the lines 4 and 5 and the overall catalyst usage is therefore 2% based on the diethoxymethane fed. The total amount of diethoxymethane fed is preferably in about 50% molar excess of the amount of ketene passed; lower or higher ratios of ketene to diethoxymethane may be used if desired.

The ketene, on being fed into the column, enters the zone 7 (the iirst Zone) in which the concentration of the boron triuoride-diethyl ether complex is 2%. Ethyl 3ethoxypropionate, produced by the reaction of ketene land diethoxymethane passes in liquid form together with unreacted diethoxymethane down column 2 and may be removed from the base of the column by line 6. The ethyl 3-ethoxypropionate produced is substantially free from ketene.

Unreacted ketene from the zone 7 passes up the column 2 and enters the zone 8 (the second zone) in which the concentration of catalyst is and is sufficient to convert completely the ketene passing into the zone.

If, in contrast to this embodiment of the present invention, all the diethoxymethane used in the process is fed into the `column 2 by the line 4, that is at the head of the column, the line 5 being closed, by feeding in the ketone by the line 1 and maintaining the column temperature at 50 C., as in the embodiment of the invention described in the previous paragraph, it is found that when a 2% catalyst concentration in the column is employed, by feeding in diethoxymethane containing 2% by weight of the boron triuoride-diethyl ether complex catalyst, the other conditions being the same, only about 40% of the ketene fed into the column is consumed; the unreacted ketone, which passes out of the column 2 by the line 9, can be recovered for recycling to the column only with great difficulty. It is found that it is necessary to have a catalyst concentration in the column of at least about 5% to ensure that all the ketene fed into the column is consumed, and this proportion of catalyst renders the process economically impracticable.

In a further embodiment of the invention, illustrated by FIGURE 2 of the drawings accompanying this specication, ketene and diethoxymethane are reacted in the presence of boron triiiuoride-diethyl ether complex as catalyst to produce ethyl-3ethoxypropionate, the process being carried out in a series of pot-reactors arranged in a cascade series.

Ketene vapour is fed by line 10 into the reactor 11, which is the first of a group of reactors 11, 12 and 13 arranged in a cascade series. Diethoxymethane is fed into the reactors 11, 12 and 13 by lines 14, 15 and 16 respectively. The average catalyst concentration in the group of reactors 11, 12 and 13 is arranged to be insuicient to convert all the ketene passing through the group of reactors to the desired product. Unreacted ketene from reactor 111, is passed to the next reactor 12 by line 17; unreacted ketene from reactor 12 is passed to the next reactor 13 by line 18, and unreacted ketene from reactor 13 is passed through line 19 to the reactor 20, which is the first of a group o-f reactors 20, .21 and 22 arranged in a cascade series connected by lines 27 and 28. A mixture of ethyl-3ethoxypropionate, diethoxymethane and catalyst from reactor .13 passes as liquid through line 1S to reactor 12, and then, from reactor 12, passes as liquid through line '17 to reactor 11, from which liquid may be removed by the line 26. Diethoxymethane and catalyst are fed as a mixture into the reactors 20, 21 and 22 by lines 23, 24 and 25 respectively. The concentration of catalyst in the diethoxymethane fed, which may be the same or different, is arranged so that the average catalyst concentration in the group of reactors 20, 21 and 22 is suicient to convert all the ketene passing through the group of reactors to the desired product. The reactor 22 has an outlet line 29. The ethyl S-ethoxypropionate produced in reactors 20, 21 and 22 passes together with the catalyst and unreacted diethoxymethane, as liquid through the series of reactors 11, 12 and 13 and ethyl 3ethoxy prcpionate may then be removed as liquid from reactor 11 by line 26. Using any suitable known method, the boron triuoride catalyst may be recovered from the reaction product leaving reactor 11 by line 26. lf desired, any excess of diethoxymethane may readily be separated from the ethyl -ethoxyp-ropionate and recycled to the reactors.

The group of reactors 11, 12 and 13 thus forms the rst Zone and the group of reactors 20, 21 and 22 forms the second zone, these zones being characterising features of the present invention.

The temperature of each of the reactors 1.1, 12, 13, 20, 21 and 22 may be the same or different; conveniently, the average temperature of the reactors 20, 21 and 22 is below the average temperature of the reactors 11, 12 and 13.

The following examples illustrate embodiments of the present invention.

Example l Ketene at the rate of 19,000 parts by volume per hour was passed into a lirst reactor, having a working capacity of 1,000 parts by volume and containing a stirred mixture maintained at `60 C. and consisting of diethoxymethane, boron triuoride-diethyl ether complex as catalyst and the product of the reaction of ketene and diethoxymethane. The gas leaving this reactor was passed into a second reactor, maintained at 15 C. and having a working capacity of parts by volume. The gas leaving the second reactor was analysed for ketene.

Diethoxymethane containing 10% by weight of boron triuoride-diethyl ether complex was fed continuously into the second reactor. The overilow from the second reactor was diluted with a further quantity of diethoxymethane so that the concentration of the boron triuoride-diethyl ether complex was decreased to 0.8% 'by Weight; this mixture was fed continuously into the first reactor, the average catalyst concentration was therefore 0.8% by weight of the diethoxymethane fed. The overflow from the irst reactor was neutralised with ammonia and the ethyl 3- ethoxypropionate Was recovered from the excess of diethoxymethane.

When the conditions in the two reactors had become steady, the conversion of diethoxymethane was 57.6% and the yield of ethyl 3-ethoxypropionate was 85.7% based on the 4diethoxymethane consumed. Of the ketene feed only 0.5% by volume remained in the gas leaving the second reactor and the yield of ethyl 3-ethoxypropionate. was 86.3% based on the ketene fed.

Example 2 Ketene gas was passed for 4.25 hours at 19,500 parts by volume per hour into a rst reactor, having a working capacity of 136 parts by volume, maintained at 45 to 50 C. and containing a stirred equilibrium reaction mixture of diethoxymethane, boron triuoridediethy1 ether complex as catalyst and the product of the reaction of ketone and diethoxymethane. The gas leaving this reactor was passed into a second reactor, maintained at 11.5 to 14.5 C. and having a working capacity of 100 parts by volume. The gaseous material leaving the second reactor was analysed for ketene.

Diethoxymethane containing 5% by weight of boron trifluoride-diethyl ether complex was fed continuously into the second reactor at 60 parts by volume per hour. The overow from the second reactor was diluted with a further quantity of diethoxymethane so that the concentration of the boron trifluoride-diethyl ether complex was decreased to 2% by weight; this mixture was fed continuously into the first reactor. The average catalyst concentration was therefore 2% by Weight of the diethoxymethane fed. The overow from the rst reactor was neutralised with ammonia and the ethyl 3-ethoxypropionate was recovered from the excess of diethoxymethane.

The conversion of the diethoxymethane to ethyl 3- ethoxypropionate was 50%, the yield of ethyl 3-ethoxypropionate being 86% based on the ketene fed and 87% based on the diethoxymethane consumed. 98% of the ketene fed was absorbed.

Similar results are achieved if the ketene is reacted, in accordance with the invention, with dialkoxymethanes other than diethoxymethane; the alkyl groups of the dialkoxymethane may be, for instance, methyl, propyl or butyl groups.

I claim:

1. In a procs of reacting a liquid lower dialkoxymethane with ketene in the presence of a boron triuoride catalyst the predetermined concentration of which corresponds to maximum yield of lower alkyl-3-lower alkoxy-propionate, the improvement consisting of mixing -a portion of the dialkoxymethane with ketene in a first zone containing said catalyst in a concentration below the aforesaid predetermined concentration, withdrawing the resultant gaseous material containing unreacted ketene from said rst zone, and mixing said gaseous material with another portion of said dialkoxymethane in a second zone containing said catalyst in said predetermined concentration.

2. The process claimed in claim 1 wherein the catalyst is boron triliuoride.

3. The process claimed in claim 1 wherein the second zone is maintained at a lower temperature than is the rst zone.

4. The improvement as claimed in claim 1, wherein said borontriuoride catalyst is selected from the .group consisting of boron triluoride and the diethylether complex of boron triuoride.

5. In a process of reacting diethoxymethane with ketene in the presence of boron triuoride catalyst the concentration of which corresponds to maximum yield of ethyl-3-ethoxypropionate, the improvement consisting of mixing a portion of diethoxymethane with ketene in a fir-st zone containing said catalyst in a concentration below the aforesaid predetermined concentration, withdrawing the resultant gaseous material containing unreacted ketene from said first zone, and mixing said gaseous material with another portion of diethoxymethane in a second zone containing said catalyst in said predetermined concentration.

6. The combination of process steps as claimed in claim 5, wherein said catalyst is borontriuoride, and wherein said predetermined concentration of the catalyst is 5%, by weight, based on thev amount of dioxymethane.

7. T'he combination of process steps as claimed in claim 6, wherein the catalyst concentration is said rst zone is 2% by weight, based on the amount of dioxymethane.

8. The combination of process steps as claimed in claim I6, wherein the iirst zone is maintained at an average temperature of about C. and the second zone is maintained at an average temperature of about 15 C.

9. The combination of process steps` as claimed in claim 5, wherein said catalyst is borontrifluoride, and wherein said predetermined concentration of the catalyst is from about 5 to 10% by Weight, based on the amount of dioxymethane.

10. The combination of process steps as claimed in claim 9, wherein the catalyst concentration in said iirst zone is from about 0.8 to 2% by weight, based on the amount of dioxymethane.

References Cited in the tile of this patent UNITED STATES PATENTS 2,039,344 Putnam et al. May 5, 1936 2,436,286 Brooks Feb. 17, 1948 2,449,447 Brooks Sept. 14, 1948 2,838,561 Fisher et al. June 10, 1958 

1. IN A PROCESS OF REACTING A LIQUID LOWER DIALKOXYMETHANE WITH KETENE IN THE PRESENCE OF A BORON TRIFLUORIDE CATALYST THE PREDETERMINED CONCENTRATION OF WHICH CORRESPONDS TO MAXIMUM YIELD OF LOWER ALKYL-3-LOWER ALKOXY-PROPIONATE, THE IMPROVEMENT CONSISTING OF MIXING A PORTION OF THE DIALKOXYMETHANE WITH KETENE IN A FIRST ZONE CONTAINING SAID CATALYST IN A CONCENTRATION BELOW THE AFORESAID PREDETERMINED CONCENTRATION, WITHDRAWING THE RESULTANT GASEOUS MATERIAL CONTAINING UNREACTED KETENE FROM SAID FIRST ZONE, AND MIXING SAID GASEOUS MATERIAL WITH ANOTHER PORTION OF SAID DIALKOXYMETHANE IN A SECOND ZONE CONTAINING SAID CATALYST IN SAID PREDETERMINED CONCENTRATION. 